1. Field of the Invention
The present invention relates to bone fixation devices for the stabilization, orientation and fusion of diseased joints (arthrodesis) or surgical cuts in bone (osteotomies).
2. Description of the Related Art
Repair of bone fractures, osteotomies, or the joining of two bone across a joint are long practiced medical techniques. Often these repairs can be facilitated by immobilization with a splint or cast but often require surgical exposure of the bone and fixation with biocompatible implants designed to reduce (bring together) and hold two or more bony structures.
Wire fixation wires, pins, screws, staples, plates and rods have a long history of use. In spite of these technologies healing sometimes does not occur and the anatomy of the healed bone is often abnormal. The prior art is replete with examples of devices that hold the bones together, but is more limited in references to those devices that present a goal of achieving anatomical adjustments.
In the prior art, U.S. Pat. No. 6,127,597 to Beyar describes systems for the percutaneous bone and spinal stabilization, fixation and repair through using devices that are placed in the medullary cavity of bone and expanded to engage and hold the bone segments. Described are self expanding implants, implants expandable by external power, and solid phase formation devices that expand. Though some of the embodiments utilize shape memory metals such as nitinol as the mechanism for expansion all suffer from a limited ability to provide fixation to the bone segments or anatomical correction.
U.S. Pat. No. 6,773,437 B2 describes a shape memory metal fixation staple and method for correcting deformities of the growing adolescent but does not correct the patient's anatomy through the use of the implant, but restricts the growth of a portion of the spine so that the deformity is corrected over years as the child grows. Once the correction is achieved, the implants are removed. This fixation implant that has an anatomical goal suffers from the delay in the correction and the removal of the implant. The implant alone does not achieve the anatomical correction, the growth of the skeleton does.
Implants that provide fixation and anatomical correction of the spine are described in U.S. Pat. No. 6,264,656 B1, U.S. Pat. No. 6,923,830 B2 and U.S. Pat. No. 7,003,394 B2 by Michelson; U.S. Pat. No. 6,743,255 B2 by Ferree and U.S. Pat. No. 6,656,178 B1 by Veldhuizen, and there are several that expand U.S. Pat. No. 6,488,710 by Besselink, U.S. Pat. No. 6,835,206 B2 by Jackson, and U.S. Pat. No. 7,018,415 B1 by McKay, but are all limited in use by the static nature of their anatomical correction, fixation elements that are separate components or fixation elements that are limited in their fixation ability, such as grooves, slots, ridges or external threads. Though these devices have fixation features and an anatomical form factor they have a history of failure due to the poor fixation ability of external threads, slots and rough surfaces and are limited by their form so as to fit the anatomy versus effect the anatomy.
The subject invention overcomes the history or poor fixation with these types of devices and allows the surgeon to effect the anatomy and relative position of the bone segments by actively changing the implant shape in the spinal disk space or space between bone created with an osteotomy or resection of a joint.